This invention relates generally to alcohol distillation and, in particular, to the removal of substantially all water from an alcohol-containing solution leaving substantially anhydrous alcohol suitable for gasohol and other industrial applications.
Alcohols, generically, are compounds having the formula ROH, in which R is any alkyl or substituted alkyl group. Alcohols may be primary, secondary or tertiary. They may be straight chains or cyclic.
Ethyl alcohol, ordinarily termed "alcohol," is one of the simplest of these alcohols . . . and one of the most important. Its uses are so many and varied that it literally can be said to be indispensable in our lives. Industrial applications include use as solvents for lacquers, varnishes, perfumes and flavorings and use as media for chemical reactions and recrystalizations. More direct uses are in "alcoholic" beverages, in the medical field and as fuels for lamps, burners and the like. One burgeoning use of great magnitude is for mixing with gasoline to produce gasohol for fueling internal combustion engines such as those powering automobiles, trucks and tractors.
Industrial production of ethyl alcohol is generally by one of three processes . . . esterification-hydrolysis, direct hydration, or fermentation of carbohydrates. Of these, fermentation is by far the greatest commercial producer and the only method used for on-the-farm production of ethyl alcohol for gasohol or motor fuel. It involves the decomposition, i.e., fermentation, of sugars in the presence of yeasts into alcohol and carbon dioxide. Commercial sources for these sugars are molasses obtained from sugarcane and starches found in potatoes and various grains such as corn, rye, rice and barley. The solution obtained from the fermentation process is commonly called "beer," in which ethyl alcohol is present as about an 8-10% solution. This highly aqueous beer solution is not usable as a motor fuel or motor fuel additive. Nearly all of the water fraction must first be removed.
To refine the beer solution into usable alcohol, the mixture is purified by fractional distillation.
Distillation, in general, involves producing a gas or vapor from a liquid by heating the same in a vessel and then collecting and condensing the vapors back into liquid form. Fractional distillation adds the feature of returning a portion of the condensate to a column on top of a still to effect a reflux and countercurrent contact with the rising vapor. Various impurities may also be removed during this fractional distillation process. Some of these may be aldehydes, ketones and other low-boiling impurities and fusel oils and other high-boiling constituents. The usual end product of this distillation at atmospheric pressure is a mixture of 95% alcohol and 5% water, known simply as 95% alcohol. It has many uses including being usable directly as a motor fuel in certain vehicles, particularly those used in modern farming operations. However, it is not acceptable as a motor fuel additive, as it still contains too much water and will separate from gasoline at usual ambient temperatures.
To avoid this problem, there is a need for "absolute alcohol," meaning a substantially anhydrous ethyl alcohol having no more than trace amounts of water in solution. Demand for this material has greatly increased in recent years along with anxieties over decreasing petroleum supplies and the skyrocketing price of gasoline in this country. Gasohol, a generic name for a mixture of gasoline and absolute alcohol, currently preferred in a 90% to 10% proportion by volume, has received much publicity as the panacea in future years as oil supplies dwindle ever more rapidly. The 95% alcohol product alone is not practicable for this use because it requires a third component such as benzene or ether to permit a stable mix with gasoline for use in internal combustion engines. Absolute alcohol requires no such additional blending agent, as it is miscible with gasoline in all proportions.
With the ready availability of 95% alcohol through distillation, it might be expected that obtaining 100% (water free) alcohol would provide little problem. This is not the case. For no matter how efficient or long the distillation process, 95% alcohol or any lower-strength solution cannot be further concentrated beyond about a 96.4% alcohol solution by weight under standard conditions. At approximately that point, an equilibrium is reached in which the liquid and vapor mixtures have the same composition. This is called an azeotrope or a constant-boiling mixture. In the case of ethyl alcohol, this is a binary azeotrope of the minimum-boiling variety. It has been reported that pressure changes affect this azeotropic mixture. Theoretically, complete separation of ethanol and water has been reported to be possible at 70 mm Hg and about 28.degree. C. That same report [(J. PERRY, CHEMICAL ENGINEERS' HANDBOOK, 631 (3rd Ed. 1950)] conditions its conclusion on the assumption that "the [tabulated] data are correct," and further states that complete separation on a commercial scale has been found "difficult to achieve." Applicant is also aware of no such successful application of this principle prior to his present invention.
To satisfy the ever-growing demand for absolute alcohol on a commercial scale, several continuous methods have been used. The first, based on a patent issued to Donald B. Keyes, U.S. Pat. No. 1,830,469, relies upon the dehydration of ethyl alcohol by the formation of a ternary azeotrope with benzene, ethyl alcohol and the remaining water in a 95% alcohol solution. This azeotropic mixture, having a low boiling point, is distilled off and must be separated by further secondary operations, leaving anhydrous ethyl alcohol at the bottom of the rectification column. Many other compounds have been suggested for use in similar azeotropic distillations, including ethyl ether, methylene chloride, isobutylene, isooctane, gasoline, benzene and naptha, isopropyl ether, methyl alcohol and acetone. All of these distillations suffer from similar problems, however, those being increased cost and increased danger from fire or explosion during processing due to the added components.
A second process, based on a patent to Joseph Van Ruymbeke, U.S. Pat. No. 1,459,699, relies upon a reflux of glycerine in the column to act as a dehydrating agent. The glycerine and water purportedly pass out at the bottom of the still with the distillate being anhydrous ethyl alcohol. Considerable alcohol is caught up with the glycerine and water, however, and must be recovered in a second rectifying still.
Yet another method, reported to be the earliest of its kind, utilizes anhydrous potassium carbonate as the drying agent. Many other inorganic compounds have been similarly studied, such as calcium oxide, calcium carbide, calcium sulfate, calcium aluminum oxide, aluminum and mercuric chloride, zinc chloride and sodium hydroxide, some of which are suggested as additives in the glycerine refluxing process mentioned above.
The immediate need for a practicable method for making substantially anhydrous alcohol is possibly greatest with the private farmer. He is experiencing ever-increasing costs, not the least of which is the cost of gasoline and diesel fuel to operate his farm machinery. At the same time, he has an available supply (and often surplus) of grains which can readily be fermented to produce a beer solution low in alcohol content. He needs to be able to concentrate that solution into a usable motor fuel and motor fuel additive. In all of the above processes, a farmer must use chemical processing equipment not usually found on a farm. For example, in distillation of alcohol he would normally use an open-fired still or a boiler for steam generation and would use well water for cooling. The use of such equipment for the processing of flammable solvents such as ethyl alcohol, particularly in concentrated form, is not a safe operation under usual farm conditions.
The end result of all of this is that no safe practicable process for making substantially anhydrous alcohol has yet been discovered which is suitable for operation by the average farmer or other person relatively unskilled in chemical technology. The known processes are complex, require other additives (such as benzene or ether) which significantly increase cost and potential hazard during use, and fail to provide a safe, efficient, simple method of operation. The applicant's invention described and claimed hereinbelow attempts to meet this need.